Tested for Purity and Potency Supports Well Being and Recovery Helps Control Appetite Tested Free of "Peak X" Dietary Supplement Product produced in a GMP certified facility. 5-HTP (5-Hydroxytryptophan) is the immediate precursor to serotonin (5-HT, 5-hydroxytryptamine). Serotonin plays an important role in the regulation of mood, appetite, body temperature, and the secretion of various hormones.